Most passenger automobiles currently manufactured have so-called driver's seat and front-passenger's seat air-bags installed therein that, when the front side of the an automobile collides with another automobile or an obstacle (head-on collision), rapidly inflates a bag between the passenger and an automobile interior structure to ensure the safety of the occupant.
In recent years, more and more automobiles include a curtain air-bag system mounted thereto to protect the head and other parts of the occupant not only in case of the head-on collision but also in a case where the side of the automobile collides with another automobile or an obstacle (side collision). The curtain air-bag system is stored as folded in the ceiling section above the side window sections or in the pillar sections of an automobile, and inflates so as to cover the side window sections upon a collision.
In such an air-bag, it is required to keep a high deployment speed upon deployment and inflation to cover the occupant protection area earlier, and reduce the injury criterion value against a human body.
Patent Literature 1 discloses an air-bag which includes an inflation portion formed in an occupant protection area and a sub-chamber formed outside the protection area, as means of reducing the injury criterion value against the occupant upon occupant restraint by the air-bag.
However, in an air-bag including a sub-chamber in communication with the protection area as described in Patent Literature 1, since gas inflows to the sub-chamber in a stage where the pressure of the inflation portion has not sufficiently risen, it was necessary to increase the capacity of the inflator to raise the pressure of the inflation portion to a sufficient pressure for occupant restraint.
Patent Literature 2 discloses an air-bag including a communication portion between a cushion chamber which is inflated by introduction of gas, and an internal pressure control chamber, in which ventilation control means which opens when the gas pressure in the cushion chamber becomes not less than a predetermined value is provided in the communication portion.
However, it is not easy to control variation of the pressure upon opening the communication portion with the ventilation control means as shown in Patent Literature 2, which is formed by adhesion by an adhesive, welding, or suturing with a suture.